1. Field of the Invention
This invention is in the field of seals for fluids; more particularly, the invention relates to seals for use in rotary pumps, engines, and the like.
2. Description of the Prior Art
Devices for handling fluids in various ways are known in the art, and are useful in many applications, such as in compressors, pumps, and external and internal combustion engines.
In recent years, rotary engines have been the subject of a great deal of engineering development. The most prominent among these is an internal-combustion engine commonly called the Wankel. This engine comprises a rotary member mounted on eccentric bearings, and operating in a trochoidal chamber. Rotation of the rotary member is kept in phase by the use of phasing gears, one of which is a stationary reaction gear fixed to the end cover plates mounted concentrically with the mainshaft.
Because of the simplicity of construction, the Wankel-type engine offers many advantages such as long life, low vibration, and high power-to-weight ratio. However, there are some problems with this engine which have persisted despite considerable effort spent on their solution. The principal one among these is that of seals in general, and apex and corner seals in particular.
The apex seal in a Wankel engine is generally a strip of material with a high hardness rating and/or a low friction value when used in the combustion chamber, where it rubs along the interior wall thereof. An example of such a material is graphite, suitably held by a metallic support, whereby both low friction and good material strength are provided, as described in U.S. Pat. No. 3,235,171. Many other materials have been used, among them high-chrome alloys, and the like.
Apex and corner seals serve the function of restricting fluid (gases in the case of rotary (Wankel) engines) to a particular portion of the apparatus. A considerable amount of effort has been expended in the attempt to provide such seals which will maintain a reasonable uniform and effective barrier to the working fluid, typically a gaseous mixture. One approach has been such as is described in U.S. Pat. No. 3,711,229 to Kurio, where the apex seal means is assisted by corner seals which are biased against the chamber wall by springs bearing on the rotary member.
Another problem common to seals for rotary engines, pumps, and the like, is the wear on the seal, which allows fluid or gas blow-by and lubricant leakage when it becomes extreme. This in itself would not be a severe drawback, assuming a reasonable life with respect to the running time of the engine or pump, since the problem of seal replacement is of the same approximate magnitude as that of ring replacement in a piston engine or compressor. However, one aspect of seal wear has been manifested in nonuniformity; that is, seals may wear in a fashion which permits the face or edge of the seal to conform to a shape different from the optimum configuration, which, in turn, may lead to pressure loss, excessive oil consumption, or both.
The problem of lubrication of seals of the type under discussion is an acute one, presenting considerations which must be taken into account when choosing a seal. Without any lubrication, of course, heat and friction would quickly destroy the seal and severely wear the chamber wall. Lubrication must be supplied, but it must be done in an economical manner, which is to say that a film of oil has to be present, but that a bath of oil would be wasteful.
Systems are known in this field which compensate for mechanical wear, such as by the use of wedge- or trapezoidal- shaped members, and the like, which displace longitudinally of the seal. There are also means for permitting a certain latitude in manufacturing tolerances. However, there have been no seal systems heretofore capable of compensating well for thermal expansion and contraction with their resulting unpredictable side effects. Necessarily, then, no seal system has yet been able to compensate for all of these variables.
With reference particularly to rotary-combustion engines, e.g., the Wankel, it is well-known among those skilled in the art that such engines can produce unacceptably high quantities of noxious emissions under various conditions which can occur readily due either to the construction or the operation of these engines. For example, if an apex seal is used which has gaps in the seal line, blow-by of unburned hydrocarbon results, and these materials then are emitted into the atmosphere unless some sort of post-combustion treatment is applied. Similarly, where gaps occur in the seal line or where the seal is worn from use, the leakage of hydrocarbon reduces combustion efficiency and temperature.
A further source of hydrocarbon emissions in some rotary-combustion engines is the use of oil-metering arrangements to provide lubrication to apex and corner seals. Because of the need to maintain a film of oil between the chamber wall and the seal, the oil must be supplied in appropriate fashion. In earlier designs, this was done by providing oil under pressure to the seal area itself; however, in most seal configurations, either geometry or economics dictate that the oil be supplied by admixture with the fuel. In these cases, some of the oil tends to be carried out unburned with the exhaust gases, obviously resulting in a detriment to the environment.
With all of the problems mentioned hereinabove, a concomitant effect is the lowering of the fuel economy of rotary-combusion engines below the optimum level otherwise possible. With improved seals, blow-by would be decreased, and over-all efficiency increased, leading them to improved fuel economy.